This invention relates to compositions and methods for removing unwanted deposits or build-up on surfaces of fluid delivery system and particularly for cleaning enclosed fluid delivery systems.
Large quantities of fluids with suspended, dispersed or dissolved materials (hereinafter referred to as "Carried Materials") are circulated through fluid delivery systems and over time the material may deposit or settle on various interior surfaces of the fluid delivery system. For example, paint is circulated and usually recirculated in piping of paint delivery systems for painting automobiles in automobile manufacturing plants. During the course of normal operation, the Carried Materials of a fluid may build up or deposit on the inside of paint fluid delivery systems, especially in areas of reduced flow such as in filters, tees, elbows and valves. This is especially true for ultrafilter membrane filters used in the electrocoat coating or painting systems. As a consequence fluid delivery systems are cleaned on a periodic basis to remove the unwanted Carried Materials adhering to the insides of pipes, tubing, filters and/or valves.
When the fluid delivery systems are cleaned, it may be necessary to remove all residual Carried Materials to avoid the rapid fouling of the system which can occur if the residual Carried Materials are available for contamination. In the case of electrocoat ultrafilters, the residual paint can plug the pores of the membrane and prevent the filter from removing contaminants from the circulated electrocoat paint. Since these systems are enclosed, removal of unwanted paint adhering to the insides of tubes, pipes and other conduits is difficult to achieve because access is difficult, and, in fact, frequently it is difficult even to determine the extent of cleaning.
A major problem that is encountered in cleaning paint fluid delivery systems is the complete removal of the cleaning materials from the system after the cleaning materials have completed their task. The art teaches the use of abrasive materials such as sand, mica and polymeric particulates. The art also teaches the use of insoluble nonabrasive materials such as "sponge-balls". However, if these materials are not completely removed from the system, they become contaminants in the paint system. These cleaning materials can be subsequently carried through the piping by the paint to the paint applicator and deposited on the object or ware to be painted along with the paint forming paint defects commonly referred to as "dirt in the paint". In other words, the cleaning materials can cause the same problems as the unwanted paint deposited on the inside of the piping of the system.
Conventionally, enclosed cathodic electrocoat paint systems are cleaned by circulation of known cleaning agents such as water, other solvents, surfactants, and organic acids, while enclosed anionic electrocoat systems are cleaned by circulating water, other solvents, surfactants, and acceptable sources of alkalinity such as sodium hydroxide and/or various amines. Circulation and recirculation in either case may take place under pressure and may be conducted for up to 48 hours or more. However, these methods often fail to remove all of the deposited paint materials in the system.
Frequently, electrocoat paint systems include membrane filters or ultrafilters whose purpose is to remove low molecular weight contaminants and impurities. These may have found their way into the paint or the system from a previous treatment step for the ware, particularly metal pretreatment chemicals such as chromates, phosphates, and other compounds such as chlorides and sulfates; such water soluble salts are removed by the ultrafilters together with water. The ultrafilters are usually tubular or spiral wound in design, and paint and other residue or Carried Materials can become coated on the inside surface of the membranes causing the ultrafilters to lose efficiency or become so clogged that the filters stop working altogether.
The electrocoat ultrafilters must be cleaned along with the rest of the system and are generally subjected to more or less the same kind of recirculation cleaning, either in place in the system, or after being isolated so the recirculative effect is concentrated on them. In spite of special treatment in many cases, the conventional cleaning compositions frequently do not remove all the paint as well as various contaminants which may be lodged quite tenaciously in the membrane. A good description of membrane filters and their cleaning can be found in U.S. Pat. No. 4,153,545 to Zwack and Christenson. Recirculation of cleaning materials is commonly practiced also in systems not including ultrafilters.
In U.S. Pat. No. 4,968,447, Dixon and Maxwell acknowledge the prior use of cleaning compositions for paint fluid delivery systems including such abrasive particles as sand and mica, which, they note, tend to settle and remain in the system to cause numerous problems; also, being highly abrasive, these materials cause unnecessary wear. In addition, such abrasives present a disposal problem when they are recovered from the system. Dixon and Maxwell go on to propose the use of polymeric particulates made of polypropylene, polyethylene, polyvinylchloride, polytetrafluoroethylene, and various other organic hydrophobic polymers and copolymers. Although these particulates do not settle out readily and can generally be rinsed from the system and incinerated, their removal from the system must still be complete. A procedure must be in place to assure that all the particulates are recovered or they can become contaminants of the system just like the old paint deposits they are trying to remove.
ABCOR Corporation teaches a method of cleaning electrocoat system ultrafilters using insoluble, nonabrasive sponge-balls which can be forced through the system including the microfilters. The purpose of the sponge-balls is to scrub the inner walls of the tubing and filters like a sponge. Of course, the sponge-balls must all be removed from the system to complete the cleaning or the system could become plugged by any remaining sponge-balls.
The rheological additive "Viscotrol", available from Mooney Chemicals, Inc. of Cleveland, Ohio, is, we understand, a particulate derivative of castor oil, apparently lightly crosslinked, which may be added to a recirculating paint cleaning system to act as a mild abrasive. After use, their removal from the system is assured by introducing an alcohol or other solvent which is absorbed by the particles, causing them to swell so they may be readily separated by filtering. "Viscotrol" is referred to as a "rheological material" by Bergishagen et al. in U.S. Pat. No. 5,443,748, which employs it in several examples for cleaning paint delivery systems of a type with which we are concerned.
In spite of the above known compositions and techniques, the cleaning art for fluid delivery systems for fluids with Carried Materials is in need of a better way to remove as completely as possible the deposits and build-up from the tubes, piping, pumps and filters of the fluid delivery systems. It would be desirable to provide cleaning methods and compositions that would completely clean the old deposits and buildup from the inside of such fluid delivery systems and which would remove as completely as possible the cleaning materials from the system so that the cleaning compositions would not become contaminants of the fluid delivery system.